The current thinking with those manufacturers is to design the bullet with a more fragile front end to enable more consistent expansion over a wider velocity range, and to intentionally lose petals to increase internal damage as it travels through the body cavity with a resultant smaller frontal area to better insure complete penetration...it's all good.
I haven’t been impressed with damage caused by loosing the petals, in fact I haven’t seen any real indication that they add anything.
